In U.S. Pat. No. 3,643,041, there is disclosed a switchplate formed on a continuous flat metal sheet having a plurality of dome-shaped resilient deformable dimples therein. The dimples are convex upward. Downward pressure, such as applied through a key device by an operator's finger, is resisted until a certain predetermined force is exerted, whereupon the dimple "collapses" with a "snap" action, resulting in the convex portion of the dimple becoming concave and the dimple contacting a fixed contact button located therebeneath.
In an example of the dimensions of the dimples, the patent teaches that the dimples may be approximately 1/2 inch in diameter and have a maximum height of approximately 0.03 inch. Due to the "snap" action that is required with the deformable dimples, the maximum height of the dimples must be limited. The height limit is directly related to the diameter of the dimples. In cases where travel of the dimples past the sheet defining the dimples of greater than 0.03 inch is required to produce switching, the diameter of the dimples must be increased. However, in conventional typewriter keyboards where such dimples can be used for switching the center-to-center spacing of the keys is 3/4 inch. Thus, the diameter of the dimples cannot be increased much beyond 1/2 inch where the switchplate is to be used as a component of a keyboard.
A snap action switch having relatively long tongue members is described in U.S. Pat. No. 3,800,104. The tongue members have free ends and fixed ends amounting to a design complexity undesirable in a simple keyboard application. Also, the construction of the tongue members does not provide close center-to-center switch spacing. Accordingly, there is a need for snap type switching members of relatively simple design which have a large effective diameter but may be located with a close center-to-center spacing.